1. Field of the Invention
The present invention pertains generally to posts, more particularly to posts that are to be driven into the ground for supporting, for example, one or more horizontal strands of wire so as to construct a fence, and especially to longitudinally slotted tubular post of triangular cross section.
2. State of the Prior Art
Metallic fence posts have been in common use for many decades. Likely, they were developed to achieve a more durable fence than can be had using traditional wooden posts. Examples of early metallic tubular fence posts are found in U.S. Pat. No. 296,070 to Rutz, U.S. Pat. No. 319,277 to Lesher and U.S. Pat. No. 620,950 to Morgan. More recent fence posts are shown in U.S. Pat. No. 3,161,263 to Stokes, U.S. Pat. No. 3,305,985 to Dean and U.S. Pat. No. 1,202,988 to Freeze.
More pertinent to the present invention are the structure set forth in U.S. Pat. Nos. 1,791,331 to Sollenberger, 1,477,349 to Hindmarsh et al. and in U.S. Pat. No. 772,662 to Mallory. The first two of these references show tubular posts fashioned of sheet metal having longitudinal slots for receiving fasteners such as U-shaped staples which may be used to secure wire fence strands to the post. In the case of the Mallory reference, the staples are intended to secure dry wall panels or equivalent wall covering material rather than fence wires, to the post structure. However, if the Sollenberger structure can be fabricated, which is doubtful because of the overturned wire flange within the tubular post, the fastener is held solely by whatever clamping force is exerted by the overturned flange. In the Hindmarsh et al. structure the staple is held in place solely by an interlocking of the slot edges in the post with the grooves in the staple; there is no substantial clamping action of the post on the staples. The Mallory metal stud, being intended to support rigid drywall panels is designed receiver with slots which fasteners that make only point contact with the slot edges. While this may be adequate where sheet material is stapled to the stud, it is not sufficient for holding wire or a small panel, or indeed an thing which does not substantially support or stabilize the staple.
Metal fence posts are exposed to extreme variations in outdoor temperature, ranging from below freezing to well above 100 degrees F., inducing severe expansion and contraction cycles of the fence post material and the fasteners held therein, which for such design as previously described commonly lead to loosening and eventual loss of the wire staples. This process is aggravated by loading of the post and wires by livestock and similar forces. A continuing need therefore exists for low-cost metal posts of sturdy, readily manufactured construction capable of holding fasteners securely and dependably over the seasons against the various loads commonly applied to them.